My 2010 developed the dreaded brake issue

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by buster71, May 23, 2025 at 11:47 AM.

  1. buster71

    buster71 Junior Member

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    I have a 2010 (purchased used in 2013 with 18k miles) that has just crossed over 200k miles.

    2 weeks ago, while coming out of a parking spot, my brakes went all weird, almost causing me to hit the car behind me while reversing, and the usual warning lights (Brake, VSC, ABS) lit up. Drove home and, parked and took to Google where I learned about the known problems with the ABS system. Coincidentally, yesterday my car refused to start, so I purchased/installed a new 12V Optima Yellow Top battery - (I was surprised that the original battery manufactured in 04/2010 made it this far!). I had hopes that the failing 12V was the cause of the brake pump issue, but it still remains.

    I have discovered, quite accidentally, that if I press the brake pedal to the floor and hold it there for about 20-30 seconds, the warning lights disappear and braking function/feel returns to normal. This will last for about 10 miles or so until the lights back come on again. Once this happens, I can hold the pedal to the floor again to clear the lights. Why does this happen? Should note that even when the lights clear and the brake again feels normal, I can still hear the pump off off every 10 seconds or so.

    I am now at the point where I need to decide whether to take the car in for diagnosis/repair or just move on from this car. It's been a great car with no major problems until now, and I always told myself I just want to make it to 200k miles, but I fear other problems may start popping up at this age/mileage. Any general advice on anything I can try - I'm most curious about why I can clear the issue by flooring the brake pedal. Also, I am only "moderately ok" with car repair so this doesn't seem like a job I would take on myself if replacement is necessary. Thanks for any help
     
    #1 buster71, May 23, 2025 at 11:47 AM
  2. ChapmanF

    ChapmanF Senior Member

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    For good measure, it wouldn't hurt to post your trouble codes here. We can probably guess some of them, but it is always good to be sure. If you don't have a scan tool to get them, then here's how:

    Blink (a/k/a Flash) Codes – How to. | PriusChat

    Kind of a curiosity about the pressure building up to adequate if you have the pedal floored. Use of the brakes changes valve positions in the actuator, and you might be valving off a path where the heaviest internal leakage is occurring. You haven't discovered any kind of special magic, and brake pressure that reaches adequate 20–30 seconds after you floor the pedal might not be enough some day when you want it sooner.

    The pump cycling (without use of the brakes) normally doesn't exceed a few times an hour in a healthy system, so a system where it is cycling every 10 seconds is not just a system that's shot, but one that's been shot for a long time, just now becoming extra obvious.
     
    #2 ChapmanF, May 23, 2025 at 12:03 PM
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  3. buster71

    buster71 Junior Member

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    I posted in the wrong forum. My car is a Gen 3 Hatchback
     
    #3 buster71, May 23, 2025 at 12:45 PM
  4. Tideland Prius

    Tideland Prius Moderator of the North
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    Moved.
     
    #4 Tideland Prius, May 23, 2025 at 7:29 PM
  5. buster71

    buster71 Junior Member

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    Thank you for moving the thread here.

    I plugged in an old ScanGauge and it did not find any error codes.
     
    #5 buster71, May 23, 2025 at 7:31 PM
  6. Dave1UK

    Dave1UK Junior Member

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    Not to hijack the OPs thread, what is considered normal operation of the pump? What is considered abnormal/nearing potential replacement? Read elsewhere that opening the door causes the pump to run? Should the pump run at all when the car is switched off?
     
    #6 Dave1UK, May 25, 2025 at 6:46 PM
  7. ChapmanF

    ChapmanF Senior Member

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    When the car is on, the pump runs as often as it needs to so the brake fluid pressure in the accumulator stays good.

    That normally means it will run every few times you have used the brakes. If you are not using the brakes at all, it may run a couple times an hour to compensate for a normal very slow loss of pressure.

    It normally doesn't run when the car is off, but starting in gen 2 they had it wake up as soon as the driver's door is opened, so it can check whether the accumulator pressure is low and, if so, get a head start on pumping it back up while you are sitting down and getting ready to push the power button.

    As there's normally enough slow pressure loss to make the pump run a couple times an hour, then if the car has been sitting turned off for a matter of hours, it is quite normal for the pump to run the next time the driver's door is opened.

    If it runs more often than that and no one's been using the brakes, there is a pressure loss issue developing. If it runs every few minutes with nobody using the brakes, it's bad. If it runs every few seconds with nobody using the brakes, it's awful.
     
    #7 ChapmanF, May 25, 2025 at 7:25 PM
  8. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    An old scangauge does not know how to interrogate most of the computers in a Prius, so if the problem isn't ignition or fuel-injection related it'll give you a false clean bill of health.

    You'll need something else. Autel AP200 or AP2500 work well for this.
     
    #8 Leadfoot J. McCoalroller, May 25, 2025 at 9:34 PM
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